1. Field of the Invention
The invention concerns a drive system, especially for a motor vehicle.
2. Description of the Related Art
In city traffic, internal combustion engines of motor vehicles run a considerable portion of their operating time in idling, due to frequent stops at traffic lights and intersections. This represents a considerable waste of resources and a burden on the environment, since it entails a needless additional expenditure of fuel with concomitant emission of toxic, climate-active, or otherwise harmful exhaust gases.
In order to lessen these needless idling phases, passenger cars have already been implemented with a so-called automatic start-stop system. In this case, the engine is automatically stopped when a particular stop condition occurs (e.g., vehicle standstill and engine idling), for example, by interrupting the fuel supply. Upon occurrence of a particular start condition (e.g., activation of the gas pedal or engaging of a gear), the engine is then automatically started again by means of the electric starter of the vehicle. Such drive systems with automatic start-stop system are known, for example, from the following publications: EP 0 233 738 A1 (LUCAS), DE 33 43 018 C1 (MITSUBISHI), DE 44 21 512 C1 (VW).
Although known drive systems with automatic start-stop system basically work and apparently accomplish a reduction in the overall fuel consumption, they also have problems which have impeded their popularization thus far: the traditional starters used produce a relatively loud starting noise, which is mainly due to the gear noises of the pinion translation of the highly geared starter motor (the transmission ratio is generally 1:10 to 1:20). Whereas in traditional motor vehicles without automatic start-stop system the starter is only seldom activated and therefore the loud starter noise is tolerated, the automatic start-stop system with the then frequent activation of the starter leads to a noise nuisance for the passengers and residents in the vicinity of traffic lights and intersections. Furthermore, the traditional starter with its magnetic switch, pinion, single-track features, and electric motor is subject to unusually large wear and tear during the frequent activation, which a conventionally designed starter can hardly withstand; therefore, in known drive systems with automatic start-stop system, a truck starter is used--which is quite overdimensioned.
The book D. Henneberger "Electrical Engine Equipment", Braunschweig 1990, pp. 98-103, proposes a flywheel starter-generator, whose rotor is a flywheel, which sits in the drive train of a motor vehicle on the takeoff shaft between engine and transmission and which can be decoupled from these by means of couplings. For starting, the decoupled--and therefore idling--flywheel is first accelerated as an electric motor. The actual starting process then occurs at a sufficient rotary speed for the starting (e.g., 1000 rpm) by fast closing of the coupling with the engine. In this way, the flywheel is braked and the engine's crankshaft is accelerated until both reach a common mean rotary speed (e.g., 500 rpm) and self-starting of the engine occurs.
Features of this flywheel-starter-generator are, first, limitation of the energy available for starting and the relatively long dead time (namely, the acceleration of the flywheel from standstill to sufficient speed for the starting takes around 3 s), which hinders a starting under nonideal conditions and several consecutive starting attempts, and secondly the clutch noise caused by the coupling to the engine at high relative speeds and the also concomitant friction losses, which detract from the efficiency and--in the case of several consecutive starting events--can also result in a heat overload of the coupling. Although the book mentions the possibility of a start/stop function, the proposed flywheel-starter-generator seems little suited for this, on account of the above-mentioned properties. A similar flywheel starter with start/stop function is known from DE 37 43 289 A1 (LuK).
The following publications are cited as further state of the art: EP 0 151 935 A1, DE 30 48 972 C2, DE 39 26 054 A1, U.S. Pat. No. 6,323,743, DE 44 12 438 C1, DE 43 44 053, DE 43 18 949 C1, DE 33 38 548 A1, DE 33 35 923 A1, DE 32 30 121 A1, DE 43 11 697 A1, DE 37 43 289 A1, DE 42 02 082 A1, DE 40 00 678 A1, U.S. Pat. No. 4,346,773, DE 33 38 548 A1, DE 44 37 322 A1, DE 28 55 886 A1, DE 42 25 683 A1, DE 32 43 513 A1, DE 38 14 484 A1, DE 44 08 719 C1, DE 23 724 B2, DE 44 04 791 C1, journal "Kraftfahrzeugtechnik", 11/82, p. 346-347.